Method for pressure molding



Dec. 18, 1945. c. c. MISFELDT 2,391,182 I METHOD FOR PRESSURE MOLDING IFiled Jan. 26, 1942 .INVENTOR. C/mgLEs C. MSF'ELDT Patented Dec. 1a,1945 1 UNITED STATE s -rn'l'lana'r OFFICE mrmon Fon massuaa MommaCharles 0. Misfeldt, Glendale, Calif. Application January as, 1942,Serial No. 423,147

2 Gaims. (01. 22-200) My invention relates to pressure molding and morparticularly to a means and method for pressure molding plastics andmetals which re- ;sults in articles having many of the characteristlcsof drop-forgings, with special reference to the uniformity andperfection of the molded product.

My invention is applicable for use in conjunction with die-castingmachines with dies modified to use my invention, and may also be used inconjunction with the extrusion molding machine shown, described andclaimed in my-prior application, Serial No. 406,254, filed August 11,1941,

Patent No. 2,356,338, August 22', 1944, of which the present applicationis a continuation-in-part.-

In said prior application I have described a machine and method ofoperating that machine whereby molten or plastic metal may be forcedinto a die under pressure, with a final and higher pressure beingapplied to th metal just before it freezes. This higher pressureprevents the formation a: large grain size in the molded prodnot, andhas a-tendency to reduce the occurrence of air bubbles orother defectsin the molded product.

The main object of my invention is to provide I a means and method ofproducing improved pressure castings without flaws, inclusions, coldshuts, or shrinkage cracks.

My invention possesses numerous other objects and'features of advantage,some of which,

together withthe foregoing, will be set forth in the followingdescription of specific apparatus embodying and utilizing my novelmethod. It is therefore to be understood that my method is apimpart tothe metal after it has filled the die, a higher pressure just at thetime of freezing of ,the metal in order to reduce grain size, to workthe metal, and to impart additional strength thereto. The latter conceptis fully described and claimed in my prior filed application citedabove;

The main difierence in handling plastic metal and molten metal residesin the pressures applied, both for forcing the metal into the die andfor the final upsetting pressure. It will be obvious from a perusal ofthe description of my present specification, that my present method andap- 5 thefinal molded product. Oxidized metal in the molded article isthus entirely eliminated, cold sheets are eliminated, and nothing butclean, non-oxidized metal is present in the article to be molded.Temperatures in the metal of the article are equalized, reducingshrinkage cracks.

plicable to other apparatus, and that-I do not limit myself in any wayto the apparatus of the present application, as I may adopt variousother apparatus embodiments, utilizing the method within the scope ofthe appended claims.

Broadly as to apparatus, my invention comprises a split die having amain cavity therein shaped in the form of a final molded product. In

addition to this .main cavity, however, I provide additional blindcavities in the die connected with the main cavity at strategiclocations, so that the entering metal, after flowing throughthe maincavity, will pass on through the main cavity Thus, the first metal I andinto the blind cavities. cooled or oxidized by passing. through the die,is trapped in the blind cavities and does not form part of the articleas finally molded. Means may also be provided to force the metal intothe die either in molten or plastic condition, as may be desired, andpreferably means are provided to Furthermore, I may prefer to form as aninlet to the article cavity, a cavity region defining the outlines of atest bar, so that after the article has been molded the test bar can beremoved from the article and subjected to yield point tests or to anyother test for which such bars may be valuable.

Articles made in accordance with my invention have suillcient strengthto be acceptable in place of sand-castings even though made on astandard die-casting machine, or, in some instances, when higherpressures are used in place of drop-forgings. The means and methoddescribed herein has greatly loweredthe rejection percentage of suchparts as are made by my means and method for aircraft use, for example,where the slightest .fiaw in the article causes rejection. Such inspection is usually made by X-raying every part before use, and in oneparticular instance rejections fell from 2-3% to 1 s of 1% when mypresent invention was added to the die and process of production of thesame part. In the drawing:

Fig. 1 is a cross-sectional view of a portion of a machine which may beutilized to practice my method, this ngure being a substantial duplicateof Fig. of my prior filed application cited clude my present invention.

Fig. 2 is a perspective view above, with modification of the die cavityto in-- or an article molded in accordance with my present inventionshowing an article as removed from the mold and before trimming.

My invention may be more readily understood by, direct reference to thedrawing-which shows one preferred form of apparatus for performingpressure piston being hollow and provided withv a movable insert a, tipa of which is utilized to close the end of piston 5. Piston I alsoslides through a loading block ll attached by bolts I! to press block I,loading block 5 I having a loading entrance I therein opening upwardlyto receive molten metal. The opposite side of press block I is providedwith a die positioning plate I! having an aperture I6 thereinregistering with the cavity 0 of the pressure cylinder, this diepositioning plate being attached to press block -I by bolts l1.Shoulders I! are provided on die positioning block it, registering withone half 20 of a split die 2|, the other half 22 thereof registeringwith a heating block 24, this heating block being in contact with apiston head 2!, sliding in ways It on the main frame 21 of the machineto which press block I is attached. Piston-head '25 is operated by ahydraulic piston rod 28 to force the two halves of the die togetherunder pressure during the molding procedure.

Die positioning block I! and heating block 24 are both heated byelectric heating elements 20. Thus, the pressure cavity 6 is heated. andboth halves of thedie block are. heated.

plates, is received either in.

a,soi.isa

I' prefer to inject the the die slowly. and the metal levelin the dieexpels die without atomization. fiowing into the die, whichwiththeairinthodieasitforoesthe. or the die between the mating surfaceslateral fins it or in and II. Naturally,

. die, a

l. to bemolded therein.

Referring againto Pig. 2, I have diagrammaticallyillustratedonthetopsurface oiend l! certainfiowmarks ll visibletothenakcdey'eoninrspectlon of the end. The mere fact that such marks show on the surfaceof the metal indicates that the metal is not homogeneous at that point.The marks are due to oxidized metal mixing with the purer metal. Underordinary circumstances shuts in ribs a and end 4|. at times end it willThe split die 2| is provided with an interior cavity Ill having at oneend an inlet II registering with aperture l8 and pressure cavity 8. Theshape of the main die cavity 30 is, .of course, the shape of the articleto be molded. However, I also provide auxiliary and preferably blindcavities in the split die, the position of which can be most readilyseenby inspection of the final molded article as shown in Fig. 2. InFig. 2, the article. portion 30' is shaped by the contour of the maindie cavity 30. The inlet ll of the die cavity is connected directly toa, test rod portion of the cavity in which a test rod 35' is moldedbetween the inlet and the article, this test rod having enlargedportions 36 at each end thereof, and a narrower portion 31 intermediatethe enlarged portions.

Along the edges of the main cavity 3| are positioned lateral cavitiesseparated from the main cavity. 30 bya small clearance only between thedie plates, so that when the die is full, lateral ribs 38 of substantialthickness are, formed attached to article 30' by thin fins 88'. The diemetal also may be forced through the cavities forming ribs it, to formlateral fins 39, which are of course paper thin where the metal entersbetween die plates 20 and 22. The cavities which form ribs 38 are madeto be of substantial volume,

and to hold a substantial amount of metal.

At the upper end or the die, as I prefer to mount the die in a verticalposition, I form a blind cavity Ill communicating with the main cavshowvery definite cold shuts due to premature cooling of the metal flowinginto it. In any case,-

the main cavity II fills only with clean, hot metal, and the perfectionof the articles molded is greatly increased as to percentage oi rejects.

After the article as shown in Fig. 2 has been removed from the die, thetest bar SI may be removed from the article by.cutting along dotted line42 at the junction of the article and the test bar portion, ribs II aretrimmed from the article and end ll is removed by cutting along line 43.This removed metal may be refined and reused. The article may then becleaned up for final use and holes bored in accordance with die marks44, if desired. No finishing is over the surfaces other than those thathave been cut or trimmed, as the final pressure in the die provides thearticle with its final finish.

While I have described my invention as applied to a particular moldedpart and with a particular arrangement of blind cavities to receive thefirst metal passing through the mold, it will mold, will vary greatly inaccordance with the shape or the article. It is believed, however, thatthe teachings of the present application are sufilcient for anyoneskilled in the art to position such blind cavities in the properpositions around the main cavity in accordance with the flow oi themetal therethrough, so that these blind cavifed to displace excess metalfrom said mold into said closed cavity against the continuouslyincreasing air pressure therein, whereby the metal in the mold cavity isdensifled and the softer metal therein is intimately and uniformlydis-r.

tributed throughout the mass of the metal forming the shaped article andexpressing excess metal including any containing occluded air and morecompletely cooled metal into said closed cavity.

2. The process according to claim 1 wherein the mold cavity has anextension outside the shaped portion, whereby there is formed anintegral portion adapted to form a test bar which maybe severed from theshaped product without injury to the contour thereof.

CHARLES c. MISFELDT.

